The present invention relates generally to ink-jet printing technology methods and apparatus and, more specifically, to a method and apparatus for aligning ink-jet pens firing droplets of a colorless fluid.
The art of ink-jet technology is relatively well developed. Commercial products such as computer printers, graphics plotters, copiers, and facsimile machines employ ink-jet technology for producing hard copy. The basics of this technology are disclosed, for example, in various articles in the Hewlett-Packard Journal, Vol. 36, No. 5 (May 1985); Vol. 39, No. 4 (August 1988); Vol. 39, No. 5 (October 1988); Vol. 43, No. 4 (August 1992); Vol. 43, No. 6 (December 1992); and Vol. 45, No. 1 (February 1994) editions. Ink-jet devices are also described by W. J. Lloyd and H. T. Taub in Output Hardcopy Devices, chapter 13, R. C. Durbeck and S. Sherr, eds., Academic Press, San Diego (1988).
In U.S. Pat. No. 5,635,969, entitled xe2x80x9cMethod and Apparatus for the Application of Multipart Ink-Jet Ink Chemistryxe2x80x9d, issued to Allen and assigned to the common assignee of the present invention and incorporated herein by reference, a multi-color ink-jet printing system includes a printing element for apply a precisely metered quantity of a colorless precursor to a recording medium surface. The precursor conditions the medium surface prior to application of one or more colorants to the recording medium surface to prevent cockle and curl and to reduce dry time, while conditioning the recording medium surface for uniform dot gain independent of media composition. See also, e.g., U.S. patent application Ser. No. 09/069,717, entitled xe2x80x9cReactive Ink Set For Ink-Jet Printingxe2x80x9d, by Askeland et al, and U.S. patent application Ser. No. 09/069,616, entitled xe2x80x9cMulti-Chamber Fluid Supplyxe2x80x9d, by Askeland et al., and Related Applications cited therein which are also assigned to the common assignee of the present invention and are incorporated herein by reference. Hereinafter, colorless fluids used to affect ink dry time and permanence and to prevent cockle and curl of the print medium are generically referred to as xe2x80x9cfixers.xe2x80x9d
In U.S. Pat. No. 5,600,350, entitled xe2x80x9cMultiple Inkjet Print Cartridge Alignment by Scanning a Reference Pattern and Sampling Same with Reference to a Position Encoderxe2x80x9d, issued to Cobbs et al and assigned to the common assignee of the present invention and incorporated herein by reference, a method and apparatus for multiple ink-jet print cartridge alignment is provided by scanning a reference pattern and sampling with an optical sensor. In effect, a given test pattern is printed and actual print image data is compared to determine any misregistration of the cartridges. See also U.S. Pat. No. 5,796,414, entitled xe2x80x9cA System and Method for Establishing Positional Accuracy in Two Dimensions Based on a Sensor Scan in One Dimensionxe2x80x9d, issued to Sievert et al and assigned to the common assignee herein and incorporated by reference.
In such two-part ink-jet printing where the colorless xe2x80x9cfixerxe2x80x9d is used to help immobilize the colored or black ink, the xe2x80x9cfixerxe2x80x9d pen is expected to deposit the colorless fluid in a precise imagewise fashion. Misdirected or missing (misfiring or plugged) nozzles will produce an inferior image with inferior image uniformity and permanence. Since the fixer fluid deposited is colorless, the image is essentially invisible. Thus, it is difficult, if not impossible, to detect such misdirected or missing nozzles. Thus, there is a need for a method and apparatus for aligning an ink-jet print cartridge which prints a colorless fluid on the print medium for permitting detection of misdirected and/or missing nozzles.
In accordance with the present invention, by including a colorless or essentially colorless chemical marker in the fixer, then the fixer deposit can be evaluated. The chemical marker is essentially colorless in the visible electromagnetic spectrum, but is detectable under certain, specified conditions. For example, either ultraviolet light absorbing/visible light (blue) emitting markers or red (or infrared) light absorbing/infrared emitting markers may be used. The blue light emission can be observed visually or electronically using UV-sensitive cameras/sensors and the IR can be detected using IR-sensitive cameras/sensors. These markers would be useful any time nozzle health is of interest. The chemical marker can also be used in color (non-black) inks that do not strongly absorb in the IR region of chemical marker emission.
In its basic aspects, the present invention provides a method for determining status of nozzles in at least one ink-jet fluid writing instrument (fixer and/or colorant) mounted for printing on an adjacently positioned print medium and using a predetermined pattern of printing. The method comprises the steps of:
mounting each ink-jet fluid writing instrument predetermined fixed positions relative to each other for printing pixels on the adjacently positioned print medium;
mounting a sensor device in a predetermined fixed position relative to the ink-jet fluid writing instrument(s), the sensor device having a source for emitting electromagnetic radiation at a first wavelength range and having a detector for detecting electromagnetic radiation at a second wavelength range, both wavelength ranges in a pre-selected wavelength region from infrared to ultraviolet;
providing a fluid in the ink-jet fluid writing instrument, the fluid containing an effective amount of a pre-selected chemical marker sufficient to be excited by the source at the first wavelength range to emit electromagnetic radiation at the second wavelength range that is detectable by the detector, the chemical marker and the sensor device both being operative over the same pre-selected wavelength region;
printing a predetermined pattern in predetermined target areas on a blank print medium by firing from the ink-jet fluid writing instrument; and
sensing the target area with the sensor device to obtain data representative of any misdirected or missing drops from the fluid.
In another basic aspect the present invention provides an apparatus for determining status of nozzles in a printhead of an ink-jet pen firing drops of a print liquid (fixer or colorant). The apparatus comprises:
at least one printhead for printing a predetermined pattern on a region of the print medium, with the ink-jet pen firing drops of the print liquid; and
a sensor device comprising a source portion for emitting electromagnetic radiation at a first wavelength range and a detector portion for detecting electromagnetic radiation at a second wavelength range, the sensor device operatively associated with a chemical marker contained in the liquid such that when the liquid is deposited on blank print medium, exposure of the chemical marker to the emitted electromagnetic radiation at the first wavelength range results in re-emission of the second wavelength range.